Search for 'natural folding lines' in the domain

Try to find the "natural folding lines" between areas in the domain.

how: ask domain experts:

"Can you imagine that changing data x ever impact data y"

eg. "[hospital] Would the patient changing family name impact which doctor they get treated by"

eg. "[webshop] Would changing the description of a product cause the price to change?"

When the domain expert looks at you like

- "You don't get it at all do you?"

Then you know you've got a 'natural folding line'

Technique: Discover service boundaries

• Apply use cases one by one

• Grow your data model + messages between

• Limit the amount of data that needs to be exchanged between services

• cluster data into services ('needs to be' together)

• • make a decision

  • most decisions will be wrong

• • every wrong decision will lead you astray

  • do it anyway

• don't name the clusters!

• • only meaningless names allowed for conciseness

  • • random colors: the green cluster, the purple cluster

    • random letters: cluster A, cluster B

  • meaningful names attract 'data related to the name'

  • • bad!

    • even when it does not need to be together

    • bad!

• once you get stuck with too much coupling, reset (or revisit a clustering decision)

You'll know when you have found the 'right' boundaries.

But you can't predict how many attempts it will take...

Pattern: Global ID

share the global ID between services

(src: Course: Advanced Distributed System Design - Udi Dahan)